1. Field of the Invention
The invention pertains to wireless communication devices. More particularly, the invention relates to antenna systems used with such devices.
2. Description of the Related Art
Wireless communication devices are becoming increasingly prevalent, with cellular telephones being a particularly notable example. With these devices, radio-frequency (RF) signals are transmitted and received to create a communication link to the device.
Most wireless communication devices contain one or more antennas protruding from a surface of the device to facilitate transmission and reception of the RF signals. Therefore, the upper surface of the device is usually the most efficient location for an antenna because this location provides the antenna the clearest path to and from the device. This antenna location also allows for some form of extendable whip antenna to be extended without interfering with the user's operation of the device. Numerous antenna systems exist which contain one or more antennas located on the upper surface of a wireless communication device.
Referring now to FIGS. 1A-1C, one type of prior art wireless communication device 90 is illustrated. FIG. 1A illustrates a frontal elevation view of a wireless communication device 90. FIG. 1B illustrates a side elevation view of the wireless communication device. FIG. 1C illustrates a top elevation view of the wireless communication device 90. The device 90 may be, for example, a cellular telephone, or other wireless communication product. The device 90 shown in FIGS. 1A-1C contains both a monopole whip antenna 92 and a helical antenna 94. The monopole whip antenna 92 extends through the center of the helical antenna 94. When the monopole whip antenna 92 is extended, the helical antenna 94 is disengaged from the transceiver and the monopole whip antenna 92 is used to transmit and receive RF signals. When the monopole whip antenna 90 is less than fully extended, the helical antenna 94 is engaged with the transceiver and the helical antenna 94 is used to transmit and receive RF signals.
Typically, the wireless communication device 90 exchanges wireless link signals with a base station. As the signals travel between the wireless communication device 90 and the base station, the signal energy of the RF signal dissipates exponentially as a function of the distance that the signal travels. In addition, the RF signals also dissipate when they pass through or reflect off of objects such as buildings, people or cars. In addition, when the helical antenna 94 is used, considerable signal loss can occur if the user's head disrupts the wireless link path between the wireless communication device 90 and the base station. When the monopole whip antenna 92 is extended, it extends up past the head of the user. However, the helical antenna 94, by nature of its small design, is more susceptible to path loss due to the user's head. For this reason, generally, the wireless communication device 90 performs better when the monopole whip antenna 92 is engaged.
Many standard wireless devices are sold today with the antenna configuration shown in FIG. 1. This configuration allows the user to operate the device with the monopole whip antenna 92 less than fully extended for the convenience of the user. For example, extending the antenna can require additional motion from the user who may wish to answer a ringing phone quickly. In addition, in certain operating conditions, such as in a crowded area or confined automobile, it is impractical to fully extend the monopole whip antenna 92. In these instances, it is common for the user to operate the wireless communication device 90 with the monopole whip antenna 92 less than fully extended.
The increase in path loss means that either the performance of the system is adversely impacted or that the transmitted signal power must be increased. Adverse changes in performance are often intolerable to system operation and can result in system failure. Increasing the transmitted signal power can result in reduced battery life, large heat dissipation problems and difficulty in meeting government signal level limit requirements. For this reasons, some systems are designed such that the user is unable to use of the helical antenna 94 to establish communication in some limited regions of the system.
It will be appreciated that there is a need in the technology for a means and method that minimizes the loss resulting from signals being forced to pass through the user's head in these circumstances.